1. Field of the Invention
The present invention is directed to computer systems; and more particularly, it is directed to the processing of digital images.
2. Description of the Related Art
Digital images may include raster graphics, vector graphics, or a combination thereof. Raster graphics data (also referred to herein as bitmaps) may be stored and manipulated as a grid of individual picture elements called pixels. A bitmap may be characterized by its width and height in pixels and also by the number of bits per pixel. Commonly, a color bitmap defined in the RGB (red, green blue) color space may comprise between one and eight bits per pixel for each of the red, green, and blue channels. An alpha channel may be used to store additional data such as per-pixel transparency values. Vector graphics data may be stored and manipulated as one or more geometric objects built with geometric primitives. The geometric primitives (e.g., points, lines, polygons, Bézier curves, and text characters) may be based upon mathematical equations to represent parts of digital images.
Digital image processing is the process of analyzing and/or modifying digital images using a computing device, e.g., a computer system. Using specialized software programs, digital images may be manipulated and transformed in a variety of ways. For example, digital images may be created and/or modified using natural media drawing and/or painting simulation. Natural media drawing and/or painting simulation refers to digital, computer-based creation techniques for creating digital drawings, digital paintings, or other digital works that attempt to mimic real-world techniques and results for drawing (e.g., using a pencil and canvas) and/or painting (e.g., using a brush, palette, and canvas).
The characteristic behaviors of real-world artist tools such as graphite pencils or oil pastels include interaction with the canvas texture, the dirtying of the tip, and the change in shape of the tip over time due to erosion. For example, during a stroke of a pencil on a canvas, a mark is made by pigment breaking off the end of the pencil graphite and becoming embedded in the canvas. Therefore, the consumption of the pigment medium is a fundamental aspect of how the tool behaves. By shaping the tip while stroking and then adjusting the tool pose to take advantage of the new shape, talented artists are able to use this effect to their advantage. For example, an artist might make many broad strokes with a pencil to create a chisel tip and then hold the pencil vertically to make a thin line with the resulting chisel edge. Although some existing digital painting applications support canvas texture and tip dirtying effects, they do not support tip erosion.